1. Field of the Invention
The present invention relates to a system for transmitting a signal for positioning. More specifically, the present invention relates to a transmitting system capable of transmitting a broadcasting signal and a signal for positioning through a common line and to a method for producing the system.
2. Description of the Background Art
The technique for obtaining positional information based on a signal transmitted from a satellite capable for transmitting a signal for positioning is known. Wile this signal can easily be received outdoors, it cannot be received indoors or Underground. Accordingly, sometimes operations of a receiving unit for the signal may not easily be checked. It should be noted that a satellite navigation system as used herein includes not only the GPS (Global Positioning System) operated by the United States, but also Galileo of which operation is currently considered by the European Union, GLONASS (Global Navigation Satellite System) operated by the Russian Federation, and any other satellite navigation systems.
For example, Japanese Patent Laying-Open No. 8-220173 discloses a pseudo GPS signal generator, which allows checking of the operation of a GPS receiving unit indoors. The generator includes a frequency converter converting a local signal sent out from a test-target GPS receiving unit to a carrier wave of an intermediate frequency range, a digital signal generator sending out a C/A (Coarse and Access) code and a navigation message, a mixer mixing the C/A code and the navigation message into the carrier wave, a noise generator sending out a white noise of a higher level than an output signal sent out from the mixer, an adder adding the white noise to the output signal from the mixer to send out a pseudo GPS signal, and an amplifier amplifying the pseudo GPS signal to a prescribed level and supplying the amplified signal to a digital signal processor accommodated in the test-target GPS receiving unit.
According to the pseudo GPS signal generator disclosed by Japanese Patent Laying-Open No. 8-220173, the digital signal processor accommodated in the test-target GPS receiving unit is supplied with the pseudo GPS signal amplified to a prescribed level by the amplifier. The pseudo GPS signal includes the carrier wave, the C/A code, the navigation message, and the white noise. The digital signal processor extracts the navigation message from the pseudo GPS signal and checks the correlation of the C/A code. Thus, the operation of a GPS receiving unit assembled indoors can be checked without installing an antenna.
While the pseudo GPS signal generator disclosed by Japanese Patent Laying-Open No. 8-220173 generates a signal for a specific purpose, i.e., for checking the operation of a newly assembled GPS receiving unit, it does not receive an actual GPS signal and transmits it indoors. Accordingly, in order to use the GPS receiving unit indoors, the GPS signal received by an antenna must be transmitted indoors and then issued indoors.
In this case, if a new system from the GPS reception antenna to a GPS signal issuing unit is constructed, installation of cables for transmitting a signal and the like are necessary. Therefore, there has been a problem that the system cannot easily be constructed indoors when costs or installability of the cables is limited.
The present invention has been made to solve the aforementioned problem, and an object thereof is to provide a system capable of issuing a signal for positioning to a receiving unit capable of receiving a signal for positioning in an area where radio waves cannot be received directly.
Another object of the present invention is to provide a system capable of issuing a signal for positioning to a receiving unit capable of receiving a signal for positioning in an area where radio waves cannot be received directly, while suppressing an increase in costs.
Still another object of the present invention is to provide a method for producing a system capable of issuing a signal for positioning to a receiving unit capable of receiving a signal for positioning in an area where radio waves cannot be received directly.
A further object of the present invention is to provide a method for producing a system capable of issuing a signal for positioning to a receiving unit capable of receiving a signal for positioning in an area where radio waves cannot be received directly, while suppressing an increase in costs.